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TCGT VS. Vertical Shear Bit...Who Will Win?

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  • TCGT VS. Vertical Shear Bit...Who Will Win?

    Found a piece of gummy 1 1/2" hot rolled bar that I had use a part of last year. At the time I had just used a known sharp HSS tool bit to obtain a pretty decent finish considering how sticky and gummy this bar seemed to be. You can see the old turned finish which is yellowed from from time and some rust preventative I sprayed on it at the time.

    So fast forward to the other day when I had this same piece chucked in the lathe and thought it might be interesting to see the difference between a new TCGT insert meant for aluminum, although they work great for a finish passes on gummy material due to it's geometry, and a HSS vertical shear bit I'd used in the past.

    I think the turning speed was about 350 rpm, the depth of cut was .002" and I used a feed rate of .003", cutting dry for both. The photo shows the TCGT side to the right near the live center and the portion turned with the vertical shear bit is to it's left.
    I'm sure I could have tweaked both of these cuts a bit but just wanted to do a quick back to back pass with all else the same except for the tooling. The cuts have not been dusted off with a rag or brush, they are as-cut.



    Reason for edit: spelling
    Last edited by Willy; 10-15-2021, 03:30 PM.
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

  • #2
    If you are looking for votes... the one on the left (shear bit) seems more shiny, more smooth.
    But it's hard to tell for sure without running my calloused, often-burnt-from-hot-steel left thumb over it.
    SE MI, USA

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    • #3
      Well, the insert cut is more 'hairy', but that might just be the light. Next step, quick, light swipe with a fine file or 400+ crocus and re-evaluate. Darn near a tie, though. If I have to grade based only on this photo, winner is HSS.
      Southwest Utah

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      • #4
        High speed tool looks better from here. Carbide tool would look better than high speed if you upped the speed and depth of cut. You should not compare the two under the same conditions. How sharp is sharp on the high speed and what geometry was tool ground. Is it exactly on center etc,etc.

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        • #5
          At that speed it's a wonder that the carbide's edge didn't get destroyed. The short cut distance probably was the saving grace. WAY too slow. At the proper speed it would have been very bright, much more so than what you got there. With such a cut you probably should have been over 1,000 SFM. Don't blame the carbide if you can't give it the correct parameters to do a proper job.

          There are ways to get a much better finish with both tools though. For another one, get that HSS honed to a keen mirror edge on every surface that touches the work or intersects with one and use a cutting oil or coolant. It is also possible to get a mirror finish with HSS but you need to run extremely slow with plenty of coolant; not a good way to do things unless it's mostly for the fun of it.
          Last edited by eKretz; 10-15-2021, 12:51 PM.

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          • #6
            As stated I knew this wasn't a fair and equal comparison and mentioned that the results could have been tweaked for both tools. Just a simple back to back test of both under less than ideal conditions for both.
            I have obtained far better results for each when optimizing parameters for the tool being used.
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia

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            • #7
              Originally posted by deltap View Post
              High speed tool looks better from here. Carbide tool would look better than high speed if you upped the speed and depth of cut. You should not compare the two under the same conditions. How sharp is sharp on the high speed and what geometry was tool ground. Is it exactly on center etc,etc.
              The HSS tool is a vertical shear bit ground to meet the general requirements of such, no need to be on-center. Very easy to grind for a finish pass tool.
              Home, down in the valley behind the Red Angus
              Bad Decisions Make Good Stories​

              Location: British Columbia

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              • #8
                I gotta agree with the others. For those conditions the shear tool still wins pretty easily. It would be interesting to run the lathe up in speed and re-cut the TCMG side again. It wouldn't take much since this is 1 1/2" stock after all. But maybe get it up to 700?
                Chilliwack BC, Canada

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                • #9
                  I'm not sure I'm "with" the folks who are immediately picking the shear bit result.

                  The problem I have with that finish is that while it is "shiny", it also looks rather grooved. More in the "highly polished, deeply scratched" sort of "look" (I have no idea if the "scratches" are real or an optical illusion. Also not at all sure that would matter, since appearance is everything).

                  The carbide surface does not show the scratches, whether they are there or not (and it seems that they should be). So it seems that it might well polish out more easily. Could be totally wrong, since we have one picture from one angle.
                  2730

                  Keep eye on ball.
                  Hashim Khan

                  Everything not impossible is compulsory

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                  • #10
                    Originally posted by BCRider View Post
                    I gotta agree with the others. For those conditions the shear tool still wins pretty easily. It would be interesting to run the lathe up in speed and re-cut the TCMG side again. It wouldn't take much since this is 1 1/2" stock after all. But maybe get it up to 700?
                    Yes totally agree, I too have achieved much better results with the TCGT and CCGT inserts, they are usually my first choice. But I love HSS and threw that in as an option for those that haven't tried the vertical shear bit as it is so easy to grind, although it too is receptive to changes in it's geometry.

                    Will have to to re-run this comparison again, this time with a higher feed rate and rpm for the TCGT and cutting oil for the vertical shear bit and perhaps some other minor tweaks. It will be a few days though before I can get back out there again, life has reared it's ugly head again with other commitments.
                    But that doesn't mean others can't jump in to toss their ugliest material to the test. All input is always welcome.

                    This was a completely last minute effort before winding down the shop the other day and thought it might provoke some thought on getting those that have difficulty obtaining a decent finish on gummy material to try something different.
                    Like a good recipe for a fine dish, we all have the right ingredients, the secret is in mixing it all together in the right proportions in order to obtain the desired results.
                    Home, down in the valley behind the Red Angus
                    Bad Decisions Make Good Stories​

                    Location: British Columbia

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                    • #11
                      The best thing for gummy steel using carbide in my experience is SPEED. Most of the time if you can't get a good finish, run faster. This becomes a problem at smaller diameters if you don't have enough RPM though. Then it can be beneficial to switch to HSS. I would be running that piece (assuming 1018 or similar) at 2,500 RPM for carbide with a light finish cut. Maybe faster with only .002" DOC. With a deeper cut you can use somewhat lower speed.
                      Last edited by eKretz; 10-15-2021, 02:37 PM.

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                      • #12
                        As others have noted, the test really isn't straight across (and it may not be possible).
                        I do think the HSS is a better finish, but I also would like to point out that the HSS won't take a .040 DOC whereas the carbide most certainly will. And the carbide will probably get the same finish at the deeper DOC too. (I would have gone 640 RPM on mine)

                        Therefore I think the carbide wins because it takes fewer passes to do the same job, but the HSS wins if the finish is the only consideration.
                        25 miles north of Buffalo NY, USA

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                        • #13
                          Originally posted by eKretz View Post
                          At that speed it's a wonder that the carbide's edge didn't get destroyed. The short cut distance probably was the saving grace. WAY too slow. At the proper speed it would have been very bright, much more so than what you got there. With such a cut you probably should have been over 1,000 SFM. Don't blame the carbide if you can't give it the correct parameters to do a proper job.

                          There are ways to get a much better finish with both tools though. For another one, get that HSS honed to a keen mirror edge on every surface that touches the work or intersects with one and use a cutting oil or coolant. It is also possible to get a mirror finish with HSS but you need to run extremely slow with plenty of coolant; not a good way to do things unless it's mostly for the fun of it.
                          In my experience Carbide seem to hold up for a loong time at slow speeds and very small DOC.(talking about these sharp xxGT inserts)

                          and these aluminum specific inserts are probably ”straight” tungsten carbide that is ill-suited for heavy&hot cuts in ferrous materials. Run them in hss speeds in ferrous materials and they last pretty well.
                          Location: Helsinki, Finland, Europe

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                          • #14
                            That is exactly how I use them: xxGT inserts in an old lathe that was designed for HSS. They do just fine in ferrous metals. The only time they have a problem is with interrupted cuts. The outside of cast iron is hard on them also. They will last forever if used in mild steel bar, in my experience.

                            Originally posted by MattiJ View Post

                            In my experience Carbide seem to hold up for a loong time at slow speeds and very small DOC.(talking about these sharp xxGT inserts)

                            and these aluminum specific inserts are probably ”straight” tungsten carbide that is ill-suited for heavy&hot cuts in ferrous materials. Run them in hss speeds in ferrous materials and they last pretty well.
                            25 miles north of Buffalo NY, USA

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                            • #15
                              Originally posted by MichaelP
                              Deeper cut and higher speed are needed to really show what finish this carbide insert is capable of.

                              At this point you only proved that carbide doesn't work well when used as HSS. With this gummy steel it worked equally bad or worse than HSS.
                              Yep, like I said before -- it wasn't a straight across test. That doesn't mean its a bad test, I don't think -- because the only thing he's looking for is the surface finish. So I gotta wonder: has anyone made a carbide shear tool? and ground a razor edge on it? Hrmmm, I gotta try that, maybe I can rig something up.
                              25 miles north of Buffalo NY, USA

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